USOS, REUSOS E ABUSOS: ATRAVESSANDO “FRONTEIRAS” E “LUSO-AFRICANIDADES” NAS HISTORIOGRAFIAS DE ANGOLA, CABO VERDE E GUINÉ-BISSAU PARA OS SÉCULOS XV, XVI E XVII

This article develops the notions of “frontier” and “Luso-Africanity”, addressing some cases anchored in the writing of the history of Angola, Cape Verde and Guinea-Bissau for the 15th, 16th and 17th centuries. The guiding thread of this narrative is the sharing and circularity of these notions, split into two moments. In the first, we will understand the notion of the Africanist frontier, as it affects the studies developed by North-American historiography since the postwar period. In a second moment, we will introduce some notions of “Luso-Africanity”, drawing attention to the focus given to multiple identity practices. At the end of this article, we will point out some of the risks and obstacles that permeate the notion of Luso-Africanity, the main one being the dissolution of the differences, asymmetries and inequalities that have crossed the Euro-African contacts. As a working hypothesis, we assume that future researches will carry out more empirical investigations, as well as support a more critical stance on cultural hybridism, blood miscegenation, multiple identities, religious syncretism and peaceful social fusion.Este artigo ensaístico destrincha as noções de “fronteira” e “luso-africanidade”, abordando alguns casos ancorados na escrita da história de Angola, Cabo Verde e Guiné-Bissau para os séculos XV, XVI e XVII. O fio condutor desta narrativa é o compartilhamento e a circularidade dessas noções, cindido em dois momentos. No primeiro, depreenderemos a noção de fronteira africanista, assim como ela incide nos estudos desenvolvidos pela historiografia norte-americana desde o pós-guerra. Em um segundo momento, introduziremos algumas noções de “luso-africanidade”, chamando atenção para o enfoque dado às práticas identitárias múltiplas. Ao término deste artigo, indicaremos alguns dos riscos e empecilhos que permeiam a noção de luso-africanidade, sendo que o principal deles é a dissolução das diferenças, assimetrias e desigualdades que percorreram os contatos euro-africanos. Como hipótese de trabalho, assumimos que futuras pesquisas realizem mais investigações empíricas, como também sustentem uma postura mais crítica a respeito do hibridismo cultural, da miscigenação sanguínea, das identidades múltiplas, do sincretismo religioso e da fusão social pacífica

Dynamic Stresses Induced within Rock in Case of Blasting with One Free Face

In this study, the behaviour of the dynamic principal stresses induced within rock by an explosion under confined condition was analyzed in case of blasting with one free face by applying the values of measured radial displacement, particle velocity and so on to equations derived from the theory of elasticity, and at the same time, the dynamic stresses on the free face were also calculated from the strain measured by the wire strain gauges affixed on the free face. The results obtained are briefly shown below. 1) The maximum stress on the free face appeared at the intersection between the free face and the burden, and its magnitude was about twice as large as the magnitude of the tangential tensile stress imparted by the incident stress wave within the range related to the breakage by blasting. 2) The maximum value of the compressive stress near the free face was decreased due to the existence of the free face, while that of the tensile stress was increased. 3) Let us consider the spherical coordinate of which origin is the center of a spherical charge. Then, at any point near the free face, the directions of the principal stresses in the γθ plane changed with time except in the direction of the burden, but at another point near an explosion point where the principal stresses were mainly composed of the stresses caused by the initial longitudinal wave, the directions of the principal stresses coincided with those of the coordinate used. 4) The maximum value of the tensile stress in φ direction was larger than those in the γθ plane on and near the free face. 5) The tensile stress caused by the Hopkinson effect appeared only near the burden. 6) It is presumed from the results of stress analysis that radial cracks will be produced in the rock mass near an explosion point, but with the approach of the free face the directions of the cracks will be curved towards the direction parallel to the free face. 7) The appearance of the breakage deduced from this investigation agrees fairly well with the practical observations

On Group Misfiring in Series Circuit Electric Blasting

In an electric blasting circuit where a large number of electric detonating caps are hooked up in a straight series, several instances have been reported in which a group of detonating caps situated in the vicinity of the middle part of the circuit were apt to misfire, and the cause of this kind of misfire has been ascribed to the leak of igniting current. Every misfire will ultimately be traceable to the lack of the amount of electric power given to the detonating cap, while in this paper, to account for one of the factors leading to the cause of such misfire, the time required for the progressing current wave to arrive at the middle part of the circuit and also the gradual decay of the intensity of current during the transition are investigated. Consequently, the intensity-time curves of igniting current and the amount of accumulated heat energy for detonating caps placed at the middle part and both ends in the circuit were studied and discussed under several feasible circuit conditions, and next, it was suggested that both the higher and the lower limits of the intensity of igniting current should be considered in order to reduce the possibility of misfire in such situations

Stress Waves and Dynamic Characteristics of Rocks under Detonator's Attack

The experiments have been carried out to investigate the characteristics of the stress waves induced in rocks when they are attacked by an explosion of a detonator and also to study some mechanical properties of rocks under such an impulsive load. To obtain the shape of a stress wave which is induced in a cylindrical bar specimen by an impulsive load, a method utilizing the displacement of the free end face of the specimen was used in this study and it was recognized that this method was simpler and more convenient than the pellet method developed by J. S. Rinehart. The change in the propagation velocity of the stress wave with distance from the shot point was studied in detail and it was found that even in the case of detonator's attack a plastic wave or a shock wave seemed to be generated in the limited region near the shot point. The dynamic stress-strain relationship and the dynamic strengths for compression and tension were determined for three kinds of rock specimens and these results were compared with those obtained by the conventional static test

On the Electromotive Force and the Electric Conductivity Accompanied with the Detonation of Explosives

The electromotive force and the electric conductivity in the ionized gases produced by the detonation of Sakura dynamite were investigated in this study. This investigation was carried out to obtain several fundamental data for developing a method by which the detonation rate of an explosive could be estimated. As to the electromotive force, the maximum values ranging from 1V to 2V were obtained and these electromotive forces were generally observed in the negative signal against the ground. In the majority of records, between 10 micro-seconds and 20 micro-seconds after detonation, the conductivity was observed to attain to its stationary value which was ranged from 5×lO⁻² mho/cm to 30×l0⁻² mho/cm